Çok Katlı Yapılara Giriş - Ders 4 - Döşeme Sistemleri

1

ÇOK KATLI YAPILARA GİRİŞÇOK KATLI YAPILARA GİRİŞÇOK KATLI YAPILARA GİRİŞÇOK KATLI YAPILARA GİRİŞ

İSTANBUL ÜNİVERSİTESİ


Dr. Kağan YEMEZ

[email protected]

2




Ders 4

�Döşeme sistemleri.–Betonarme – Çelik – Kompozit

–Tasarım kriterleri

3

İİç kolonların yerleri ç kolonların yerleri

betonarmebetonarme

çelikçelik

4

iç kolonların yerleriiç kolonların yerleri

Tali kiriTali kirişşlerler

Ana kiriAna kirişşbetonarmebetonarme

ÇelikÇelik

Tali kiriTali kirişşlerler

6 6 -- 22 m22 m

5

Structural Steelwork EurocodesStructural Steelwork EurocodesStructural Steelwork EurocodesStructural Steelwork Eurocodes

Introduction to composite Introduction to composite Introduction to composite Introduction to composite construction of buildingsconstruction of buildings

6

GeneralGeneralGeneralGeneral

These two materials complete one These two materials complete one

another:another:

SteelSteel and concreteand concrete

�� Concrete is efficient in compression and steel in Concrete is efficient in compression and steel in

tensiontensiontensiontension

�� Concrete encasement restrain steel against Concrete encasement restrain steel against

bucklingbuckling

�� Protection against corrosion and fireProtection against corrosion and fire

�� Steel bring ductility into the structureSteel bring ductility into the structure

7

GeneralGeneralGeneralGeneral

Aspects for using composite Aspects for using composite structures:structures:

�� ArchitecturalArchitectural�� ArchitecturalArchitectural

�� EconomicalEconomical

�� FunctionalityFunctionality

�� Service and FlexibilityService and Flexibility

�� AssemblyAssembly

8

Aspects for using composite Aspects for using composite

structuresstructures



Architectural:Architectural:

�� Longer spansLonger spans

�� Thinner slabsThinner slabs

�� More slender columnMore slender column

�� More generous opportunities for More generous opportunities for

designdesign

9





Economical:Economical:�� Reduction of height reduces the total of Reduction of height reduces the total of

the building the building ----> saving area of cladding> saving area of cladding

�� Longer spans with the same height Longer spans with the same height

----> column free rooms> column free rooms----> column free rooms> column free rooms

�� Additional storeys with the same Additional storeys with the same

total height of buildingtotal height of building

�� Quicker time of erection:Quicker time of erection:

�� Saving costs, earlier completion of the buildingSaving costs, earlier completion of the building

�� Lower financing costsLower financing costs

�� Ready for use earlier thus increasing Ready for use earlier thus increasing

rental incomerental income

10





Functionality:Functionality:

�� Fire protection by using principles of reinforced Fire protection by using principles of reinforced

concrete in which the concrete protects the steelconcrete in which the concrete protects the steel

11





Service and building flexibility:Service and building flexibility:

�� Adaptable structuresAdaptable structures

�� Modification during the life of the buildingModification during the life of the building

�� Modify services without violating the privacy of Modify services without violating the privacy of

other occupantsother occupants

�� Accommodation of service facilitiesAccommodation of service facilities

in the ceilingin the ceiling

within a false floorwithin a false floor

in a coffer box running along the wallsin a coffer box running along the walls

12





Assembly:Assembly:�� Working platforms of steel deckingWorking platforms of steel decking

�� Permanent shuttering Permanent shuttering

�� Reinforcement of profiled steel sheetings Reinforcement of profiled steel sheetings �� Reinforcement of profiled steel sheetings Reinforcement of profiled steel sheetings

�� Speed and simplicity of constructionSpeed and simplicity of construction

�� Quality controlled products ensure greater accuracyQuality controlled products ensure greater accuracy

13

Construction methodsConstruction methodsConstruction methodsConstruction methods

Traditionally two counteracting methods of

construction could be observed both connected with

special advantages but also disadvantages worth

mentioning.�� Conventional concrete Conventional concrete

construction methodconstruction method

�� Construction in steelConstruction in steel

construction methodconstruction method

++ freedom of form and freedom of form and

shapesshapes

++ easy to handleeasy to handle

++ thermal resistancethermal resistance

-- timetime--consuming shutteringconsuming shuttering

-- sensitive on tensile forcessensitive on tensile forces

++ high ratio between bearing high ratio between bearing

capacity and weightcapacity and weight

++ prefabricationprefabrication

++ high accuracy high accuracy

-- low fire resistancelow fire resistance

-- need of higher educated need of higher educated

personalpersonal

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Construction methodsConstruction methodsConstruction methodsConstruction methods

�� Composite ConstructionComposite Construction

comparing these two methods a combination of both comparing these two methods a combination of both

presents the most economic waypresents the most economic way

++ higher bearing capacityhigher bearing capacity++ higher bearing capacityhigher bearing capacity

++ higher stiffness higher stiffness

++ plastic redistributionplastic redistribution

15

Construction elementsConstruction elementsConstruction elementsConstruction elements

composite column floor = beam + slabcomposite beam

composite slab

16


Composite slabsComposite slabs

��Reinforced concrete slabReinforced concrete slab

in-situ concrete on shuttering partially prefabricated slabs fully prefabricated slabs

17


SlabsSlabs

��PrePre--stressed concrete slabsstressed concrete slabs

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SlabsSlabs

��Profile steel sheetingProfile steel sheeting

Interlock between steel and concreteInterlock between steel and concrete

frictionalfrictionalmechanicalmechanical

end anchorageend anchorage

19

Composite slabs comprise ofComposite slabs comprise ofComposite slabs comprise ofComposite slabs comprise of

in-situ concrete slab

reinforcement

Support beam

• steel decking

• reinforcement

• cast in situ concrete

After concrete has Support beam

After concrete has hardened:

behaves as a composite steel-concrete structural element

Profiled steel designed to act as both permanent formwork during concreting and tension reinforcement

After construction:

• profiled steel sheet

• upper concrete topping

interconnected so that horizontal shear forces can be transferred at the steel-concrete interface.

20

Profiled decking typesProfiled decking typesProfiled decking typesProfiled decking types

Numerous types with different: • shapes• depth and distance between ribs• width, lateral covering, • plane stiffeners • mechanical connections • mechanical connections Thickness : 0,75mm � 1,5mm Depth : 40mm � 80mmGalvanized on both facesCold formedCold forming causes strain

(pekleşme) hardening and increase in yield

S235 � 300 N/mm2

21

Steel to concrete connectionSteel to concrete connectionSteel to concrete connectionSteel to concrete connection

• Adhesion not sufficient to

create composite action in

the slab

Efficient connection made by:

• Mechanical anchorage from

re-entrant trough profile

bo

bb

hc

hph

Open trough profile

bo

bb

hc

hph


local deformations

• Decking shape - re-entrant

trough profile

• End anchorage provided by

welded studs

• End anchorage by

deformation of the ribs at the end of the sheeting.

( a ) mechanical anchorage ( c ) end anchorage

( b ) frictional interlock ( d ) end anchorage by deformation

22


BeamsBeams��Conventional and innovative Conventional and innovative

composite beamscomposite beams

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BeamsBeams

��Types of shear connectorsTypes of shear connectors

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Composite actionComposite actionComposite actionComposite action

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Döşemeler : yerinde dökme Döşemeler : yerinde dökme

betonarme Döşemelerbetonarme Döşemeler

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BaBaşşlıklı kamalarınlıklı kamalarınkaynaklanmasıkaynaklanması

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MetalMetaltrapeztrapeztrapeztrapezperdeperde

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Ters SehimTers Sehim

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Progress factor: steel gradesProgress factor: steel gradesProgress factor: steel gradesProgress factor: steel grades

Advantages of mixed construction and high steel grades

Type ofconstruction

non-mixed mixed mixed mixed

Steel grade S 235 S 235 S 355 S 460

Reduction in

weight of steel- 13 % 44 % 52 %

Cross-section

Beam Size HE 650 A HE 550 A IPE 550 IPE 500

Reduction in

weight of steel- 13 % 44 % 52 %

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ColumnsColumns

��Examples of composite columnsExamples of composite columns

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JointsJoints��Example of vertical shear transfer Example of vertical shear transfer

between beam and columnbetween beam and column

removed after concretingreinforcement

bracket for the lower flange

bracket with shear connectorscontact pieceweld seam

shot-fired nails

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ExamplesExamplesExamplesExamples

Millennium Tower Millennium Tower (Vienna (Vienna -- Austria)Austria)

�� 55 storeys55 storeys

�� Total height 202 mTotal height 202 m

Total ground floor 38000 m2Total ground floor 38000 m2�� Total ground floor 38000 m2Total ground floor 38000 m2

�� Capital expenditure about 145 million EuroCapital expenditure about 145 million Euro

�� Time of erection: 8 monthsTime of erection: 8 months

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42,3 m42,3 m

Composite columns

Concrete core

Composite Slim floor beams

Concrete slab

Composite frame

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Total time of erection: 8 monthTotal time of erection: 8 monthmax. speed 2 to 2.5 storeys per week!max. speed 2 to 2.5 storeys per week!

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Citibank Duisburg Citibank Duisburg (Duisburg (Duisburg -- Germany)Germany)


�� Total height 72 mTotal height 72 m

�� Total ground floor 14500 m2Total ground floor 14500 m2

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Parking deck “DEZ” Parking deck “DEZ” (Innsbruck (Innsbruck -- Austria)Austria)


�� Ground dimensions 60 x 30 mGround dimensions 60 x 30 m

�� Max. span length 10.58 m with Max. span length 10.58 m with 26 cm slim floor slab (= l/40)26 cm slim floor slab (= l/40)26 cm slim floor slab (= l/40)26 cm slim floor slab (= l/40)

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Erection of composite columns over 2 storeysErection of composite columns over 2 storeysAssembly of prefabricated concrete slabsAssembly of prefabricated concrete slabs

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260 200

Cross section of the slimCross section of the slim--floor beam and slabfloor beam and slab--200 mm concrete slab200 mm concrete slab--60 mm prefabricated concrete elements60 mm prefabricated concrete elements--steel beam:steel beam: web 165/20 mmweb 165/20 mm

flange 245/40 mmflange 245/40 mm--headed studs: 22 mmheaded studs: 22 mm

60

39

Concluding summaryConcluding summaryConcluding summaryConcluding summary

Composite construction is popular Composite construction is popular for buildings because of following for buildings because of following aspects:aspects:

�� EconomyEconomy

�� ArchitectureArchitecture

�� FunctionalityFunctionality

�� Service and building flexibilityService and building flexibility

�� AssemblyAssembly

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Dr. Kağan YEMEZ

[email protected]

Next … Introduction to EC 4

41


Introduction to EC4Introduction to EC4

42

Eurocode 4 Part 1.1Eurocode 4 Part 1.1Eurocode 4 Part 1.1Eurocode 4 Part 1.1

�Sections follow a typical design sequence:– Material properties (Malzeme özellikleri)

– Safety factors (Emniyet katsayıları)

– Methods of analysis

– Element design, ultimate and serviceability

�Some sections deal with specific topics:-– Durability

– Composite joints in frames for buildings

– Composite slabs with profiled steel sheeting

43

TerminologyTerminologyTerminologyTerminology

� A number of terms are clearly defined:– ‘COMPOSITE MEMBER’ - one with concrete and steel

interconnected components

• ‘BEAM’ - subject mainly to bending (eğilme)

• ‘COLUMN’ - subject mainly to compression• ‘COLUMN’ - subject mainly to compression

(basınç)

• ‘SLAB’ - profiled steel sheets as permanent

shuttering (kalıcı kalıp) and tensile reinforcement

(çekme donatısı)

– ‘SHEAR CONNECTION’ (kayma donatısı) - the connection between steel and concrete components

44

TerminologyTerminologyTerminologyTerminology

� ‘COMPOSITE FRAME’ - includes some composite

elements

� ‘COMPOSITE JOINT’ - reinforcement contributes to

resistance (dayanım) and stiffness (rijitlik). resistance (dayanım) and stiffness (rijitlik).

� ‘PROPPED (ALTTAN DESTEKLİ) STRUCTURE OR

MEMBER’ - weight of wet concrete carried

independently, or steel supported until concrete able

to resist stress

� ‘UNPROPPED (ALTTAN DESTEKSİZ) STRUCTURE

OR MEMBER’ - weight of wet concrete is applied to

the steel elements unsupported in the span.

45

Material PropertiesMaterial PropertiesMaterial PropertiesMaterial Properties

�Concrete– Normal and lightweight concrete as EC2

– Concrete grades less than C20/25 or greater than C60/75 excludedexcluded

�Reinforcing steel– As EC2

– Reinforcement grades with a characteristic strength greater than 550N/mm2 not covered

46

Material PropertiesMaterial PropertiesMaterial PropertiesMaterial Properties

�Structural steel– As EC3

– Steel grades with a characteristic strength greater than 460N/mm2 not covered

�Profiled steel sheeting for composite slabs�Profiled steel sheeting for composite slabs– As EC3

– Types of steel restricted

– Recommended minimum thickness is 0.7mm

�Shear connectors– Reference to ENs for material specification

47

Structural AnalysisStructural AnalysisStructural AnalysisStructural Analysis

�Ultimate Limit State (Taşıma Gücü)– Elastic or plastic global analysis allowed

– Certain conditions apply to the use of plastic analysis

�Serviceability Limit State (Servis Yüklemesi)– Elastic analysis must be used

– The effective width is as defined for the ultimate limit state, and appropriate allowances may be made for concrete cracking, creep and shrinkage

48

Elastic AnalysisElastic AnalysisElastic AnalysisElastic Analysis

� Stages of construction may need to be considered

� The stiffness of the concrete may be based on the

uncracked condition for braced structure

� In other cases, some account may need to be taken

of concrete cracking by using a reduced stiffness over

a designated length of beam

� Creep is accounted for by using appropriate values

for the modular ratio

� Shrinkage and temperature effects may be ignored

� Some redistribution of elastic bending moments is

allowed

49

Ultimate Limit StateUltimate Limit State

(Taşıma Gücü)(Taşıma Gücü)

Ultimate Limit StateUltimate Limit State

(Taşıma Gücü)(Taşıma Gücü)

�Concerned with the resistance of the structure to collapse

�Based on the strength of individual �Based on the strength of individual elements

�Overall stability of the structure must be checked

�Factored load conditions

50

BeamsBeamsBeamsBeams

�Bending resistance– Applicability of plastic, non-linear and elastic

analysis

– Full or partial interaction defined

�Vertical shear resistance– Effects of shear buckling

– Combined bending and shear

51

LateralLateral--Torsional BucklingTorsional Buckling

(Yanal Burulması Burkulma )(Yanal Burulması Burkulma )

LateralLateral--Torsional BucklingTorsional Buckling

(Yanal Burulması Burkulma )(Yanal Burulması Burkulma )

�Top flange is laterally restrained by the

concrete slab

� In hogging bending the compression flange is � In hogging bending the compression flange is

not restrained– Lateral-torsional buckling must be checked

– Under certain conditions such checks are unnecessary

52

Longitudinal Shear ConnectionLongitudinal Shear ConnectionLongitudinal Shear ConnectionLongitudinal Shear Connection

�Related to:– strength of slab and transverse reinforcement

– connector types– connector types

53

Serviceability Limit StateServiceability Limit State

(Servis Yüklemesi)(Servis Yüklemesi)

Serviceability Limit StateServiceability Limit State

(Servis Yüklemesi)(Servis Yüklemesi)

�Deflections

�Concrete cracking

�Control of vibrations and limiting �Control of vibrations and limiting stresses are not included

54

DeflectionsDeflections

(Sehim)(Sehim)

DeflectionsDeflections

(Sehim)(Sehim)

�Calculated deflection is seldom meaningful because:

– actual load unlike design load;– actual load unlike design load;

– idealised support conditions seldom realised

�But calculated deflection can provide an index of stiffness

55

DeflectionsDeflectionsDeflectionsDeflections

�Guidance is given on calculating deflections for composite beams– including allowances for partial interaction– including allowances for partial interaction

– concrete cracking

�Calculated deflections should be compared with limits in Eurocode 3 or in given standards.

56

Deflection LimitsDeflection LimitsDeflection LimitsDeflection Limits

�Six categories:– roofs generally

– roofs frequently carrying personnel other than for maintenance

– floors generally

– floors and roofs supporting plaster or other brittle finish or non-– floors and roofs supporting plaster or other brittle finish or non-flexible partitions

– floors supporting columns (unless deflection included in global analysis for ultimate limit state)

– situations in which the deflection can impair the appearance of the building

57

Calculating DeflectionsCalculating DeflectionsCalculating DeflectionsCalculating Deflections

�Steel member alone– Construction stage for for unpropped conditions

– Procedures of EC3

– Bare steel section properties

�Composite cross-section– Elastic analysis

– Suitable transformed section

– Allow for incomplete interaction and cracking of

concrete where appropriate

58

Concrete CrackingConcrete CrackingConcrete CrackingConcrete Cracking

�Concrete may crack due to:– Direct loading

– Shrinkage– Shrinkage

�Excessive cracking of the concrete can:– affect durability

– compromise appearance

– impair the proper functioning of the building

59

Concrete CrackingConcrete CrackingConcrete CrackingConcrete Cracking

� May not be critical issues

� Simplified approaches based on:

– minimum reinforcement ratios– minimum reinforcement ratios

– maximum bar spacing

– diameters

� Guidance on calculating crack widths

� Limiting crack widths related to exposure

conditions

60

Composite SlabsComposite SlabsComposite SlabsComposite Slabs

�Ultimate and serviceability limit states

�Construction stage– steel sheeting acts as permanent shuttering– steel sheeting acts as permanent shuttering

– must support wet concrete loads (unpropped)

– reference to EC3 Part 1.3

61

Composite SlabsComposite SlabsComposite SlabsComposite Slabs

�Calculation procedures for– flexure

– longitudinal shear– longitudinal shear

– vertical shear

– stiffness

– span:depth ratios

– limiting

62

Concluding SummaryConcluding SummaryConcluding SummaryConcluding Summary

� A number of terms in EC4 have a very precise

meaning

� The principal components for composite

construction are concrete, reinforcing steel,

structural steel, profiled steel sheet, and shear structural steel, profiled steel sheet, and shear

connectors

� Material properties for each component are

defined in other Eurocodes

� Guidance is given on what methods of analysis,

both global and cross-sectional, are appropriate

63

Concluding SummaryConcluding SummaryConcluding SummaryConcluding Summary

� EC4 is based on limit state design principles

� The Ultimate Limit State is concerned with

collapse (Taşıma gücü göçme ile ilgili)

� The Serviceability Limit State is concerned with The Serviceability Limit State is concerned with

operational conditions. (Servis Yüklemesi kullanım koşullarında)These relate specifically

to deflections and crack control, and EC4

provides guidance for controlling both

� EC4 is structured on the basis of element type;

detailed procedures for the design of beams,

columns and slabs are given in separate

sections.

64


Structural Modelling and DesignStructural Modelling and DesignStructural Modelling and DesignStructural Modelling and Design

65

Scope of the lectureScope of the lectureScope of the lectureScope of the lecture

�Structural modelling

�The design process�The design process

�Generalities about design requirements for main structural elements

66

Structural modellingStructural modellingStructural modellingStructural modelling

In order to overcome this difficulty:

– The slab is assumed to span in a principal direction and is designed

accordingly.

– The three-dimensional framework is then reduced to plane frames

which are studied independently each from the other.

– In order to enable such a “dissociation” into plane frames, the concept – In order to enable such a “dissociation” into plane frames, the concept

of effective width for the composite slabs is introduced.

Sonuç olarak, kompozit kiriş çelik profil ve etkilidöşeme tablasından oluşur ve birbirine kaymabirleşim elemanları ile bağlanır.

(continued)

67


Effective width of slab

« Shear lag » effects induce non uniform stress distribution in the slab

⇒ concept of “effective width” b⇒ concept of “effective width” beff

(continued)

b b b

be1be2

beff

211

68


Simple and safe recommendations in Eurocode 4:

beff = be1 + be2

with bei = min ( Lo/8; bi )

where L is the distance measured between consecutive where Lo is the distance measured between consecutive points of contraflexure in the bending moment diagram

(continued)

0,25(L + L ) 1 2 1,5L but 4 < L +0,5L )4 3 L = 0

L = 0 0,8L 1 0,7L 2 0,8L - 0,3L but > 0,7L

3 4 3

L 1 L 2 L 3 L 4

0,25(L + L ) 2 3

69


Equivalent modular ratio n

Actual composite beam cross-section replaced by an

equivalent steel section for elastic calculations.

Use of an « equivalent modular ratio n » Use of an « equivalent modular ratio n »

Ea is the elastic modulus for steel

E’c is an elastic « effective »modulus for concrete

(continued)

'c

a

E

En=

70


The transformed section

(continued)

71


Elastic strains and stresses in the composite section

(continued)

72


The E’c value is influenced by:

– the concrete grade

– the concrete age,

– the short-term or long-term character of the loading

⇒Effects of creep, shrinkage, …⇒Effects of creep, shrinkage, …

Values of E’c ond of the modular ratio n are

given in the next slide.

(continued)

73

Analysis for ultimate limit statesAnalysis for ultimate limit statesAnalysis for ultimate limit statesAnalysis for ultimate limit states

�Rough values of E’c for evaluation of n

– E’c = Ecm for short-term effects

– E’c = Ecm / 3 for long-term effects– E’c = Ecm / 3 for long-term effects

(continued)

Strength class

of concrete

20/25 25/30 30/37 35/45 40/50 45/55 50/60

Ecm (kN/mm2) 29 30,5 32 33,5 35 36 37

74

Design requirementsDesign requirementsDesign requirementsDesign requirements

�Design requirements at SLS

– Control of:

� the transverse displacements of the composite � the transverse displacements of the composite

beams

� the cracking of the concrete

� the beam vibrations, especially for large span

beams

(continued)

75


� Design requirements at ULS

– Verification of the joint resistance

– Verification of the slab resistance– Verification of the slab resistance

– Verification of the column stability and resistance

– Verification of the composite beams

(specific design checks listed on next slides)

(continued)

76


– Specific design checks for composite beams

� Resistance of critical sections defined as the points of :

� maximum bending moment (section I-I)

� maximum shear (section II-II at external supports)

� high combined bending moment and shear (sections III-III)

� sudden change of section and/or mechanical properties

P

splice

II

II

I

I

III III

III III

V

V V

IV

VI

VI

d

� sudden change of section and/or mechanical properties

(continued)

77


– Specific design checks for composite beams

� The strength of the longitudinal shear connection (line IV-IV)

� The longitudinal shear strength of the transversally reinforced concrete slab (line V-V and VI-VI)

� The resistance to lateral-torsional buckling under negative bending

P

splice

II

II

I

I

III III

III III

V V

IV

VI VI

VI VI

VII

d

� The resistance to lateral-torsional buckling under negative bending moments, with lateral displacement of the bottom flange of the steel section (buckled position VII)

78

Composite Slabs Composite Slabs

with with

Profiled Steel SheetingProfiled Steel Sheeting

Structural Steelwork EurocodesStructural Steelwork Eurocodes

Profiled Steel SheetingProfiled Steel Sheeting

79

Composite slabsComposite slabsComposite slabsComposite slabs

• One way spanning

• Typical span 3.5 m

• Span onto composite secondary

beams beams

• Secondary beams span onto primary

beams

• Rectangular grids

• Slab unsupported during construction

80

Advantages of composite slabsAdvantages of composite slabsAdvantages of composite slabsAdvantages of composite slabs

• hızlı ve basit inşaat

• aşağı katta çalışan işçileri koruyan güvenli

çalışma platformu

• betonarme döşemeden daha hafif• betonarme döşemeden daha hafif

• Genellikle hafif beton ile kullanılır

- Zati ağırlığı azaltmak için

• fabrikada prefabrik hazırlanabilen döşeme

saçları ve kirişleri

- küçük toleranslarla bile çalışılabilir.

81

Composite slabs comprise ofComposite slabs comprise ofComposite slabs comprise ofComposite slabs comprise of

in-situ concrete slab

reinforcement

Support beam

• steel decking

• reinforcement

• cast in situ concrete

After concrete has Support beam

After concrete has hardened:

behaves as a composite steel-concrete structural element

Profiled steel designed to act as both permanent formwork during concreting and tension reinforcement

After construction:

• profiled steel sheet

• upper concrete topping

interconnected so that horizontal shear forces can be transferred at the steel-concrete interface.

82

Profiled decking typesProfiled decking typesProfiled decking typesProfiled decking types

Numerous types with different: • shapes• depth and distance between ribs• width, lateral covering, • plane stiffeners • mechanical connections • mechanical connections Thickness : 0,75mm � 1,5mm Depth : 40mm � 80mmGalvanized on both facesCold formedCold forming causes strain

(pekleşme) hardening and increase in yield

S235 � 300 N/mm2

83

Steel to concrete connectionSteel to concrete connectionSteel to concrete connectionSteel to concrete connection

• Adhesion not sufficient to

create composite action in

the slab

Efficient connection made by:



bo

bb

hc

hph

Open trough profile

bo

bb

hc

hph


local deformations

• Decking shape - re-entrant

trough profile

• End anchorage provided by

welded studs

• End anchorage by

deformation of the ribs at the end of the sheeting.

( a ) mechanical anchorage ( c ) end anchorage

( b ) frictional interlock ( d ) end anchorage by deformation

84

Reinforcement in the slabReinforcement in the slabReinforcement in the slabReinforcement in the slab

Provided for:

• Load distribution of line or

point loads

• Local reinforcement of slab

openingsopenings

• Fire resistance

• Upper reinforcement in

hogging moment area

• Control cracking due to shrinkage

Mesh reinforcement

placed at the top of the profiled decking ribs.

85


Overall depth h, > 80 mm.

Thickness hc of concrete

over decking > 40mm

If the slab acts compositely

• The nominal size of

aggregate should not

exceed the least of:

0,40 hc or bo/3 or 31,5 mm

• Composite slabs require a If the slab acts compositely

with a beam, or is used as

a diaphragm

total depth h > 90mm

concrete thickness hc > 50mm

• Composite slabs require a

minimum bearing of

75mm for steel or

concrete and 100mm for other materials.


bo

bb

hc

hph

Open trough profile

bo

bb

hc

hph

86

Composite slab behaviourComposite slab behaviourComposite slab behaviourComposite slab behaviour

Perfect connection

between the concrete

and steel sheet -

complete interaction.

Phchp

P

L =L

4s L =L4s

b

ht

Relative longitudinal

displacement between

steel sheet and adjacent

concrete- incomplete

interaction.

L

L =4s L =

4s

load P

Pu

Pf

0deflection δ

First crack load

P : complete interactionu

P : partial interactionu

P : no interactionu

P P

δ

load P

Pu

Pf

First crack load



P : no interactionu

P P

δ

87

Composite slab stiffnessComposite slab stiffnessComposite slab stiffnessComposite slab stiffness

After first cracking,

frictional and mechanical

interaction begin to

develop as the first micro-slips occur.

0deflection δ

First crack load

Stiffness depends on the

effectiveness of the connection type.

From 0 to Pf , the physical-

chemical phenomena

account for most of the

initial interaction between the steel and concrete.

88

Three types of behaviourThree types of behaviourThree types of behaviourThree types of behaviour

Complete interaction:

• No global slip at the

steel-concrete interface

exists

• Failure can be brittle or

load P

Pu

Pf

First crack load



P : no interactionu

P P

δ

• Failure can be brittle or

ductile

Zero interaction:

• Global slip at the steel-

concrete interface is not

limited and there is almostno transfer of shear force.

0deflection δ

First crack load

Partial interaction:

• Global slip not zero but limited

• Shear force transfer partial and

the ultimate lies between the

ultimate loads of the previous

cases.• Failure can be brittle or ductile.

89

Composite slab stiffnessComposite slab stiffness

• Represented by the first part of the P-δ curve

• Stiffness highest for complete interaction

• Three types of link between steel and concrete:

1. Physical-chemical link:1. Physical-chemical link:

always low but exists for all profiles

2. Friction link:

develops as soon as micro slips appear

3. Mechanical anchorage link:

acts after the first slip

depends on the steel-concrete interface shape.

90

Composite slab collapse modesComposite slab collapse modesComposite slab collapse modesComposite slab collapse modes

Failure type I

applied moment exceeds Mpl.Rd

generally the critical mode for moderate to highgenerally the critical mode for moderate to high

spans with a high degree of interaction

between the steel and concrete.

III I

II

Shear span Ls

91


Failure type II

ultimate load resistance is governedby the steel concrete interface.by the steel concrete interface.

happens in section II along the shear span Ls.

III I

II

Shear span Ls

92


Failure type III

applied vertical shear exceeds shearresistance.resistance.

This is only likely to be critical for deep slabsover short spans and subject to heavy loads

III I

II

Shear span Ls

93

Brittle Brittle or or ductile failure?ductile failure?Brittle Brittle or or ductile failure?ductile failure?

• Depends on

characteristics of the steel-

concrete interface.

• Slabs with open trough

profiles experience a more

Load PDuctile behaviour

profiles experience a more

brittle behaviour

• Slabs with re-entrant

trough profiles tend to

exhibit more ductile

behaviour.

deflection δ

Brittle behaviour

• Decking producers ameliorate

brittle behaviour with various

mechanical means – embossments,

indentations, dovetails

Shear connectors

between beam and

slab influence the failure mode.

94

Design conditionsDesign conditionsDesign conditionsDesign conditions

Two design conditions should to be

considered

During construction

steel sheet acts as

shuttering

In service

concrete and steel combine to

form a single composite unitshuttering form a single composite unit

95

Construction conditionConstruction conditionConstruction conditionConstruction condition

• Steel deck must resist weight of wet concrete

and the construction loads

• Deck may be propped temporarily during

constructionconstruction

• Preferable if no propping is used

• Verification at ULS and SLS should be in

accordance with part 1.3 of Eurocode 3

• Effects of embossments or indentations on

the design resistances should be considered

96

Design (construction) at the ULSDesign (construction) at the ULSDesign (construction) at the ULSDesign (construction) at the ULS

• Weight of concrete and steel deck

• Construction loads

- weight of the operatives and concreting plant

• ‘Ponding' effect

- increased depth of concrete due to deflection• Storage load (if any)• Storage load (if any)

( b ) ( b )( a ) ( c )

3000

( b ) ( b )( a ) ( c )

3000

moment over supportMoment in mid-span

( a ) Concentration of construction loads 1,5 kN / m²

( b ) Distributed construction load 0,75 kN / m²

( c ) Self weight

! Minimum values are

not necessarily

sufficient for excessive

impact or heaping

concrete, or pipeline or

pumping loads

97

Deflection Deflection Deflection Deflection

Under self weight + the weight of wet concrete,

but excluding construction loads

δ < L/180

If δ < 1/10 of the slab depthIf δ < 1/10 of the slab depth

- ponding effect may be ignored

Allow for ponding by assuming in design

- nominal thickness of the concrete is

increased over the whole span by 0,7δ.

98

Composite slab design checksComposite slab design checksComposite slab design checksComposite slab design checks

Loads to be considered are the following :

1. Self-weight of the slab (profiled sheeting and

concrete)

2. Other permanent self-weight loads (not load

carrying elements)

3. Reactions due to the removal of the possible

propping

4. Live loads

5. Creeping, shrinkage and settlement

6. Climatic actions (temperature, wind...).

For typical buildings, temperature variations are generally not considered.

99

Serviceability limit stateServiceability limit stateServiceability limit stateServiceability limit state

1. Deflections

2. Slip between the concrete slab and the

decking at the end of the slab called end slip3. Concrete cracking

100

DeflectionsDeflectionsDeflectionsDeflections

Recommended limiting values

• L/250 permanent + variable long duration loads

• L/300 variable long duration loads

• L/350 if composite slab supports brittle elements

Deflection of the sheeting due to its own weight and

the wet concrete need not be included

101

SummarySummarySummarySummary

• Composite slabs are widely used in steel framed

buildings

• Steel deck acts as

- shuttering during construction

- steel reinforcement for the concrete slab. - steel reinforcement for the concrete slab.

• Design of composite slabs requires

consideration of two conditions

1. steel deck as a relatively thin bare steel

section supporting wet concrete and

construction operatives

2. as a composite structural element in service

102

SummarySummarySummarySummary

• Performance of a composite slab is

dependent on the effectiveness of the shear

connection between the concrete and steel

sheeting.

• Longitudinal shear resistance may be

assessed by:

1. A semi-empirical design method (m-k)

2. Partial interaction theory

103




Dr. Kağan YEMEZ

[email protected]

Next…Shear Connectors and Structural Analysis

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